Sharing AGC Loop Between Demodulator and Spectrum Analysis System

ABSTRACT

Systems and methods for sharing an AGC loop between a wireless data demodulator and a spectrum analysis module that operates simultaneously with the data demodulator. In one embodiment, a predetermined hold time prevents the AGC loop from changing gain too often, thereby allowing the spectrum analysis module to collect reliable data. In another embodiment, the hold time may be extended to coincide with a spectrum analysis event, such as a boundary of an FFT block. In still another embodiment, an FFT valid signal is provided such that collected FFT blocks can be designated as suspect and then subsequently processed accordingly.

FIELD OF THE INVENTION

Embodiments of the present invention relate to systems and methods forautomatic gain control (AGC) in a device that simultaneously demodulateswireless signals and performs spectrum analysis of a band over which thewireless signals are detectable.

BACKGROUND OF THE INVENTION

The explosive growth in wireless applications and devices over the pastfew years has produced tremendous public interest benefits. Wirelessnetworks and devices have been deployed in millions of offices, homes,and more recently, in increasing numbers of public areas. These wirelessdeployments are forecast to continue at an exciting pace and offer thepromise of increased convenience and productivity.

This growth, which is taking place mostly in the unlicensed bands, isnot without its downsides. In the United States, the unlicensed bandsestablished by the FCC consist of large portions of spectrum at 2.4 GHzand at 5 GHz, which are free to use. The FCC currently sets requirementsfor the unlicensed bands such as limits on transmit power spectraldensity and limits on antenna gain. It is well recognized that asunlicensed band devices become more popular and their density in a givenarea increases, the spectrum will become overcrowded and usersatisfaction will collapse. This phenomenon has already been observed inenvironments that have a high density of wireless devices.

The types of signaling protocols used by devices in the unlicensed bandsare not designed to cooperate with signals of other types also operatingin the bands. For example, a frequency hopping signal (e.g., a signalemitted from a device that uses the Bluetooth™ communication protocol ora signal emitted from certain cordless phones) may hop into thefrequency channel of an IEEE 802.11 wireless local area network (WLAN),causing interference with operation of the WLAN. Thus, technology isneeded to exploit all of the benefits of the unlicensed band withoutdegrading the level of service that users expect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system having a traffic monitoringsection and spectrum monitoring section each having its own dedicatedradio;

FIG. 2 is a block diagram of a spectrum analysis engine and wirelessdemodulator using a shared radio in accordance with an embodiment of thepresent invention;

FIG. 3 shows a state diagram for AGC with a hold time functionimplemented in accordance with an embodiment of the present invention;

FIG. 4 is a timing diagram that shows an example of a (e.g., wireless)signal that turns on and off, and how AGC reacts at different stages inaccordance with an embodiment of the present invention, namely the statediagram of FIG. 3;

FIG. 5 shows the use of a digital variable gain amplifier (DVGA) inaccordance with an embodiment of the present invention;

FIG. 6 shows a state diagram that incorporates the use of a DVGA inaccordance with an embodiment of the present invention;

FIG. 7 is a timing diagram showing the respective gain levels of theDVGA and AGC in accordance with an embodiment of the present invention;

FIG. 8 is a timing diagram showing the use of an FFT valid signalindicative of the reliability of FFT blocks in accordance with anembodiment of the present invention;

FIG. 9 is a timing diagram that illustrates a gain change delay inaccordance with an embodiment of the present invention;

FIG. 10 is a timing diagram that illustrates how different AGC settlingtimes are applied to different processing blocks in accordance with anembodiment of the present invention;

FIG. 11 depicts the use of multiple AGC loops in accordance with anembodiment of the present invention; and

FIG. 12 is a flowchart depicting an example process in accordance withan embodiment of the present invention.

FIG. 13 depicts a timing diagram that shows how a minimum of two FFTblocks must have a same value in order to treat that value as a reliablevalue in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Overview

Embodiments of the present invention provide systems and methods forsharing a radio and an AGC loop between a wireless data demodulator anda spectrum analysis module that operates simultaneously with the datademodulator. In one embodiment, a predetermined hold time prevents theAGC loop from changing gain too often, thereby allowing the spectrumanalysis module to collect reliable data. In another embodiment, thehold time may be extended to coincide with a spectrum analysis event,such as a boundary of an FFT block. In still another embodiment, an FFTvalid signal is provided such that collected FFT blocks can bedesignated as suspect and then subsequently processed accordingly. Alsoprovided is the ability assign appropriate gain settling times todifferent components of the system. For example, a spectrum analysisclassification process might require a gain settling time that isshorter than, for example, a spectrum analysis plotting function.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a system including a spectrum analysis engine (“SAgE” or“SAGE”) that can be used to monitor a wireless channel in effort to makebetter use thereof. As shown, there is a spectrum monitoring section 100to monitor RF activity in the frequency band and a traffic monitoringsection 170 that is capable of sending and receiving traffic accordingto a communication protocol, such as an IEEE 802.11 WLAN protocol. Thespectrum monitoring section 100 comprises a radio 110 (primarily forreceive operations) that is capable of tuning to receive energy at eachchannel (or simultaneously all channels in a wideband mode) of, forexample, any of the unlicensed bands (2.4 GHz and 5 GHz) in which IEEE802.11 WLANs operate. An analog-to-digital converter (ADC) 112 iscoupled to the radio 110 and converts the downconverted signals from theradio 110 to digital signals. A radio interface (I/F) 120 is coupleddirectly to the radio 110 and also to the output of the ADC 112. Aspectrum analysis engine (SAGE) 130 is coupled to the radio I/F 120. Inone embodiment, the SAGE 130 includes a spectrum analyzer 132, a signaldetector 134 having a peak detector 136 and one or more pulse detectors138, and a snapshot buffer 140. A Fast Fourier Transform (FFT) module133 is coupled between the radio I/F 120 and the spectrum analyzer 132,or, as shown in FIG. 1, included in the spectrum analyzer 132. The SAGE130 generates spectrum activity information that is used to determinethe types of signals occurring in the frequency band, and capturessignals for location measurement operations. A dual port random accessmemory (RAM) 150 is coupled to receive the output of the SAGE 130 and aprocessor I/F 160 interfaces data output by the SAGE 130 to a processor192, and couples configuration information from the processor 192 to theSAGE 130. A memory 194 is accessible to the processor 192 for storage ofdata and program instructions.

The functions of the SAGE 130 will be briefly described in furtherdetail hereinafter. The spectrum analyzer 132 generates datarepresenting a real-time spectrogram of a bandwidth of radio frequency(RF) spectrum, such as, for example, up to 100 MHz. The spectrumanalyzer 132 may be used to monitor all activity in a frequency band,for example, the 2.4-2.483 GHz ISM band, or the 5.15-5.35 GHz and5.725-5.825 GHz UNII bands (embodiments may cover a band form 4.9 to 5.9GHz). The FFT module 133 is, for example, a 256 frequency bin FFTprocessor that provides (I and Q) FFT data for each of 256 frequencybins that span the bandwidth of frequency band of interest. A spectrumcorrection block may be included to correct for I and Q channelimbalance by estimating an I-Q channel imbalance parameter related tophase error and amplitude offset between the I and Q channels, and tosuppress a side tone resulting from the RF downconversion process. Thespectrum analyzer 132 may further comprise a power computation block tooutput a power value for each FFT frequency bin. The spectrum analyzer132 may further include a statistics logic block (not shown) that haslogic to accumulate statistics for power, duty cycle, maximum power anda peaks histogram. Statistics are accumulated in the dual-port RAM 150over successive FFT time intervals or blocks. As an example, an FFTblock comprises 256 samples, implying a time interval of 6.4 μs (256/40MHz). After a certain number of FFT intervals, determined by aconfigurable value stored in control registers (not shown), an interruptis generated to output the stats from the dual-port RAM 150. Forexample, the statistics are maintained in the dual-port RAM 150 for10,000 FFT intervals before the processor reads out the values. Thepower versus frequency data generated by the spectrum analyzer 132 mayalso be used as input to the signal detector.

The signal detector 134 detects signal pulses in the frequency band andoutputs pulse event information entries, which include one or more ofthe start time, duration, power, center frequency and bandwidth of eachpulse that satisfies configurable pulse characteristic criteriaassociated with a corresponding pulse detector.

In the signal detector 134, the peak detector 136 looks for spectralpeaks in the (power versus frequency data derived from FFT blockoutput), and reports the bandwidth, center frequency and power for eachdetected peak. The output of the peak detector 136 is one or more peaksand related information. The pulse detectors 138 detect and characterizesignal pulses based on input from the peak detector 136.

The snapshot buffer 140 collects a set of raw digital signal samplesuseful for signal classification and other purposes, such as locationmeasurements. The snapshot buffer 140 can be triggered to begin samplecollection from either the signal detector 134 or from an externaltrigger source, such as a signal from the processor to capture receivedsignal data for a period of time sufficient to include a series ofsignal exchanges used for location processing explained hereinafter.Alternatively, the snapshot buffer 140 can be in a free-running statecontinuously storing captured data, and then in response to detectingthe first signal (e.g., a Probe Request frame), the snapshot buffer isput into a post-store mode that extends long enough to capture an ACKframe signal data.

The traffic monitoring section 170 monitors packet activity in awireless network, e.g., a WLAN, and sends and receives certain packetsthat are used for location measurement processes. For example, thesystem may transmit an 802.11 Probe Request frame, data frame orrequest-to-send frame that may be addressed to the device to be located.Included in the traffic monitoring section 170 are a radio transceiver172 (comprising a transmitter Tx and a receiver Rx) and a basebandsignal processor 178. The radio transceiver 172 and baseband signalprocessor 178 may be part of a package chipset available on the markettoday, such as an 802.11 WLAN chipset for any one or more of the802.11a/b/g/n or other WLAN communication standards. The baseband signalprocessor 178 is capable of performing the baseband modulation,demodulation and other PHY layer functions compliant with the one ormore communication standards of interest (e.g., IEEE 802.11a,b,g,h,etc.). An I/F 180 couples the baseband signal processor 178 and radiotransceiver 172 to the processor 192. Additional detail regarding thesystem of FIG. 1 may be found in U.S. Pat. No. 7,184,777.

While the system of FIG. 1 provides significant capabilities, the systememploys two separate radios, thereby consuming more power than may bedesired. Moreover, separate radios typically require separate chipsetsand antennas, resulting in excess use of “real estate” on circuit boardsand increased bill of materials and thus cost as well.

FIG. 2 is a block diagram depicting an embodiment of the presentinvention in which a single radio is shared between a wirelessdemodulator block and a spectrum analysis module. More specifically, asingle radio frequency (RF) receiver 202 receives over-the-airtransmissions and feeds the received signals to an analog-to-digitalconverter (ADC) 204 for digitization. The resulting digitized signalsare filtered with filters 206 and then passed, on the one hand, to ademodulator 208, such an 801.11x demodulator and, on the other hand, tospectrum analysis module 210 for simultaneous processing. Demodulator208 is used as a traffic monitoring section, like that shown in FIG. 1.Those skilled in the art will appreciate that demodulator 208 may beconfigured or designed to monitor other types of traffic includingBluetooth™ communications, among others. Although described hereinprimarily as a monitoring tool, embodiments of the instant invention mayalso be implemented as part of a WiFi access point and used to makebetter use of the radio spectrum at a given location.

Spectrum analysis module 210 may be configured similarly to spectrummonitoring section 100 of FIG. 1. A plots module 212 and aclassification module 214 are in communication with spectrum analysismodule 210 and are provided, respectively, to provide a visualrepresentation of the spectrum analysis on a display for a user to view,and to provide an indication (e.g., viewable) of the types of signalsthat are present in a given band that is being monitored by the spectrumanalysis module 210. Analyzed data may also be used to provide an “airquality” measure for a given wireless channel.

Also shown in FIG. 2 is an automatic gain control (AGC) block 220 andloop 221. As is well-known in the art, AGC is an adaptive function thatmonitors an output signal and provides feedback to gain function 203 toadjust the gain to an appropriate level for a range of input signallevels. In other words, AGC may be used to ensure that, e.g., the ADC204 is not saturated or under driven. Notably, although demodulator 208and spectrum analysis module 210 share radio 200 including AGC loop 221,demodulator 208 and spectrum analysis module 210 often have different,and sometimes competing, sets of AGC requirements.

For the demodulator 208, a typical demodulation configuration mightinclude an AGC loop to adjust (amplify or attenuate) the receive signalstrength to maximize performance of the receiver design for a specificprotocol.

Further, there is always a timing budget for different portions of theframe reception, which will drive how quickly the AGC must settle. Thisbudget allows the design to lose samples at the start of a frame, andassumes that all frames are conformant to the protocol implemented.

For the spectrum analysis module or engine 210, in conjunction with theclassification module 214, it is sometimes possible to identify anunderlying signal source based on RF signatures. With this in mind, onepossible approach to classification is to demodulate a signal or severaldifferent signals, with each protocol having different requirements onthe AGC loop.

If protocols other than the primary function of the demodulator 208 arepresent (interference), the operation of the AGC loop may be lessimportant to the modem. In one implementation, the demodulator functionis designed and optimized for reception of frames of a selected (e.g.,802.11) protocol, while consideration of other protocols is not a focusof the design. That is, the design is concerned with improving receivesensitivity for unique cases of the selected protocol, such as receivingweak frames of the protocol, or for when the protocol “punches” throughsome weaker signal.

The spectrum analysis module 210 may have different AGC requirements.For example, in one implementation, much of the spectrum analysis isfast Fourier transform (FFT) driven wherein output is computed on ablock of samples (N_(FFT)). Typically, the gain must be fixed for theduration of N_(FFT). Furthermore, any changes in signal levels during agiven FFT can cause undesired artifacts, such as spectral splatter.

Further still, multiple FFT blocks are often required to be computed fordisplay of, e.g., a “Power vs. Frequency” (PvF) plot. PvF plots areusually presented by averaging the FFTs (average trace) or computing amax of the FFTs (max trace). Gain changes during an FFT caused by theAGC 220 can lead to unreliable output. It will not only impede visualplots, but may also interfere with frequency domain pulseidentification. These effects are described in, e.g., co-pendingapplication Ser. No. 11/830,390 and U.S. Pat. No. 7,292,656.

In addition, the noise floor level of a radio will vary with gainsettings, and so frequent or large adjustments will impact detectionthresholds and the ability to detect and/or demodulate weaker signalsthat may also be present.

Also, with a wider band modem, such as for 802.11, there can often bemore than one frame, from different narrow band interferers present onthe channel at a time. In addition, some protocols have more amplitudevariation than the primary protocol, and so a faster AGC loop mightimpair the reception of such protocols.

AGC Hold Time

In general, when signal level drops beyond some threshold, aconventional AGC would normally release to a higher gain setting causingat least some of the undesirable effects on spectrum analysis describedabove when the AGC loop is shared. In order to address this problem,embodiments of the present invention provide that any release (e.g., toa higher gain) of the AGC 220 be delayed, and if the input signal comesback into range during a predetermined hold time, no adjustment to theAGC 220 gain is made. This hold time may be picked to ensure some numberof FFTs worth of data is sampled at the same gain setting, or toincrease the probability of specific header detections. Once again,although described herein primarily with respect to IEEE 802.11standards, the present invention is also applicable to other wirelessprotocols including IEEE 802.16, which is more commonly known as WiMAX.

FIG. 3 shows a state diagram for an AGC with a hold time functionimplemented in accordance with an embodiment of the present invention.The state transitions are based on the following definitions:

-   -   “agcAttackThresh” is the signal level threshold above which AGC        loop must reacquire. Input signal is too strong and the AGC must        react to lower the receive gain. A possible value may be −3        dBFS.    -   “unlockThresh” is the signal level threshold below which the AGC        is considered to have lost lock on the signal and the AGC must        reacquire. Input signal is weak and the AGC must react to        increase the gain. A possible range may be 20 dBFS to −35 dBFS.    -   “gainChngHoldOver” is the minimum amount of time that gain must        be held constant once it has been adjusted to an optimum level        with the only exception being if the signal level goes above        agcAttackThresh. Generally speaking, this needs to be low for        modem applications—e.g. <10 us for 802.11, but for spectrum        analysis this needs to be large—e.g., 150 us.    -   “agcSetPoint” is the ideal signal level at the input to the A/D,        typically around 12 dBFS.

Referring again to FIG. 3, the state transitions conditions are asfollows:

-   -   0—AGC is enabled, and the AGC moves to acquisition mode.    -   1—AGC is locked (gain optimally set for the input signal). AGC        is locked when signal level after the input to the A/D is at the        agcSetPoint.    -   2—Signal>agcAttackThresh (input signal level has increased).    -   3—Signal<unlockThresh (input signal level has decreased). Here,        the process transitions to a “Slow Release” for a        “gainChngHoldOver” time before transitioning to “Acquisition”        state. A counter (agcCounter) is started at this time.    -   4—Signal>unlockThresh and Signal<agcAttackThresh (input signal        has recovered to near its previous level).    -   5—Signal<unlockThresh for gainChngHoldOver time (input signal        level counter is reset during state transition due to condition        3).

FIG. 4 is a timing diagram that shows an example of a (e.g., wireless)signal that turns on and off and how an AGC reacts at different stagesin accordance with an embodiment of the present invention. Referring tothe lower left of FIG. 4, it can be seen that the state of AGC 220remains in “Slow Release” for a predetermined period of time thatexceeds a low power period for the input signal. The next Slow Releasestate, however, expires as the input signal power remains low for aperiod of time longer than the Slow Release period (i.e., thegainChngHoldOver time).

In the last Slow Release state example in FIG. 4, the gain of the AGC220 is constant for a period of time that is substantially equivalent toa minimum number of FFT blocks that are needed to adequately performspectrum analysis. As noted above, there is a certain minimum number,N_(FFT), of FFT blocks that may be needed to conduct spectrum analysis,e.g., 1.5 FFTs, which corresponds to 10 μs.

Digital Variable Gain Amplifier to Handle Small Gain Changes

Sometimes an AGC loop will make small gain changes, either increasing ordecreasing in gain. This may be in response to certain interferers whenthe base protocol is not detected, or specific to the normal framereception design. These changes may occur quite frequently and thuscause disruptions to simultaneous spectrum analysis.

To address this issue and maintain appropriate signal collection forpurposes of spectrum analysis, digital variable gain amplifiers (DVGAs)502 a or 502 b may be employed for either the demodulation or thespectrum analysis. Such a configuration is shown in FIG. 5, which is,except for DVGAs 502 a, 502 b, essentially identical to FIG. 2. TheseDVGAs are shown in broken lines in FIG. 5 to indicate that, typically,only one DVGA would be present in a given implementation to modify thegain for only one of the demodulator or spectrum analysis module at anygiven time. Alternatively, a single DVGA could be used where that DVGAis selectably connectable to one of the demodulator 208 or spectrumanalysis module 210. With such a configuration, rather than making asmall AGC gain change, the gain of the AGC can be held fixed, and thesamples to the demodulator 208 can be digitally adjusted (multiplied) by502 a to its “sweet spot,” while leaving spectrum analysis samplesunchanged. Similarly, if the demodulator 208 must make a small gainchange, the samples to spectrum analysis could be adjusted by 502 b tominimize the impact. The latter case is less preferable, as sometransients may be experienced.

The state diagram of FIG. 6 is a slightly modified version of the statediagram of FIG. 3. In the case of FIG. 6, a variable dgvaThresh may bedefined as the threshold below which only the DVGA gain is changed andthe RF gain (AGC loop 221) is unchanged. A new transition state may bedefined as follows for this embodiment:

-   -   6—If abs(gainChange)<dvgaThresh, then the AGC state machine        stays in “GainLock” state.

The timing diagram of FIG. 7 shows that the AGC gain remains unchangedduring a small input signal change, but that the DVGA decreases its gainfor a corresponding small increase in the input signal power.

Processing Suspect FFTs

Another issue that arises with respect to sharing a radio between ademodulator and a spectrum analysis system is that when a small gainchange is made (digital or analog), FFT transients may occur that impactlogic that is analyzing a stream of FFTs. Embodiments of the presentinvention address this phenomenon as follows. When the gain changeduring an FFT block is not near the start or end of the FFT block, thenthat FFT can be “marked” (e.g., stored with a flag, etc.) as suspect.There are several options available for subsequent use of these suspectFFTs. They can be ignored (possibly assuming prior level holds), theycan be used with less weighting than “good” or reliable FFTs, or theycan be used for detection but not for measurement. An alternate solutionwould be to abort the FFT in progress, and restart the FFT with onlygood samples.

FIG. 8 shows a timing diagram consistent with the foregoing. As shown,an “FFT Valid Signal” can be employed to distinguish the valid, “good,”or reliable FFTs from any suspect FFTs. The so-called “bad” or suspectFFTs may be so-designated in view of the gain change that occurredduring one of the FFT sample blocks.

Gain Change Coincident with Spectrum Analysis Event

Also, a small gain change or an AGC release may interrupt the FFTprocessing flow. One possible solution to this potential problem inaccordance with the present invention is to delay the gain change suchthat it aligns or coincides with a spectrum analysis event, such as anFFT block boundary. Such an implementation has the effect of minimizingthe number of suspect FFTs.

FIG. 9 depicts a timing sequence that illustrates the foregoing. Asshown, the Slow Release state is extended slightly beyond its set periodto coincide with the boundary of an FFT block. The FFT valid signaltransitions to low at the boundary, thereby including one FFT block inthe stream that might not have otherwise been included. To implementthis extended delay, a feedback signal (Safe_to_Change) from the FFTblock (i.e., 133 of FIG. 1) may be provided to indicate when it is safeto make these gain changes. The signal might be asserted for severalclocks on either side of an FFT block start (with appropriate pipelinedelays) or when an FFT is not being used. Then, the state condition (5),with respect to FIG. 3, is modified as follows:

-   -   5—Signal<unlockThresh for at least gainChngHoldOver time and        Safe_to_Change is asserted.

Gain Settling Time

A shared radio/AGC loop also introduces a potential problem of selectingan appropriate gain settling time for a particular application. That is,the gain settling time may need to be individually configured fordifferent uses. More specifically, the AGC 220 is preferably configuredto wait a predetermined amount of time before sampling to make futuregain change decisions. In accordance with an embodiment of the presentinvention, the demodulator 208, for example, may or may not use the samedelay before using samples for a receive operation—as signal acquisitionand frequency tracking impose strict requirements on the AGC.

Similarly, the spectrum analysis module 210 may need a different delaybefore samples can be used for display or detection purposes, such asfor longer DC settling times. That is, the DC correction loop may takesome time to settle after a gain change. A demodulator would be designedto handle this, but display and FFT data may be impacted by the drift.In other words, the same settling time may not be appropriate for bothfunctions for the following reason. If the settling time is too long,then demodulation may not work. One the other hand, if the settling timeis too short then a display of data may include undesirable splatters.

There is also a different delay that may be needed before samples arecaptured for post processing (e.g., for processing in the classificationmodule 214 shown in FIG. 2). For purposes of example only, typical waittimes may be less than 1 us for the demodulator 208 and classificationmodule 214, and about 5 us for plotting using plots module 212.

Different delays for the different processing blocks are shown in FIG.10. Note the delays are preferably software configurable depending onthe application/situation (and applies to both edges of gainvalid—rising/falling).

Multiple AGC Loops

Even with the implementation of independent settling times, there maystill be a problem in that sometimes the compromises with differentdelays for gain valid may impair the normal demodulation operation,while still not allowing good results for spectrum analysis in all cases

To address this issue, an embodiment of the present invention providesmultiple AGC blocks 220 a, 220 b (or loops) as shown in FIG. 11. Byhaving the ability to switch in desired AGC performance characteristicsusing multiplexer 1112, it is possible to allow configuration of the“normal” demodulator's AGC loop allowing simultaneous spectrum analysis(so that radio time can be shared for both purposes), as well as othersettings (or disabling of features) for best demodulator performancewhen spectrum analysis is not enabled. It may also be desirable to havea separate AGC loop that is optimized for spectrum analysis only, whendemodulation is not required, or for better detection of specialinterferers such as radar. Although only two AGC blocks 220 a, 220 b areshown in FIG. 11, those skilled in the art will appreciate that therecould be multiple AGC blocks, each separately configurable for aparticular purpose. Alternatively, shared loops may be provided, whereindividual loops are configurable to have selected characteristics.

FIG. 12 is a flowchart depicting an example process in accordance withan embodiment of the present invention. As shown, at step 1202, data isreceived at, e.g., a wireless receiver. At step 1204, an automatic gaincontrol (AGC) loop associated with the receiver is controlled such thatthe data is compatible with the processing requirements of both thedemodulator 208 and the spectrum analysis module 210. The data, asindicated by step 1206, is then passed from the receiver to both thedemodulator 208 and the spectrum analysis module 210 for furtherprocessing.

In another aspect of the invention, it has been observed that an FFTdisplay may show transients during a small AGC gain change, or when aninput signal starts/stops during a given FFT. FIG. 13 depicts a “minimumof two FFT” approach for reducing or eliminating the display of suchtransients. In one real-time mode of operation, a “Max trace” spectrumanalysis option tracks a maximum across the dwell of the minimum of thelast two FFTs for each frequency bin. As a result, transients that donot persist and random variation in noise are suppressed from thedisplay, without losing the detection of hoppers and burst transmitters.Limiting or eliminating altogether such transients is desirable toreduce display splatter and undesirable effects of the trace.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the systems and methodsdescribed herein consistent with the principles of the present inventionwithout departing from the scope or spirit of the invention. Althoughseveral embodiments have been described above, other variations arepossible consistent with the principles of the present invention.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of thedisclosed embodiments. The specification and examples are exemplaryonly, and the true scope and spirit of the invention is defined by thefollowing claims and their equivalents.

1. A system, comprising: a radio having a radio frequency receiver andan automatic gain control (AGC) loop; a demodulator configured todemodulate wireless traffic received by the receiver; and a spectrumanalysis module configured to perform spectrum analysis of a frequencyband over which the wireless traffic was detected, wherein the AGC loopis configured to allow the demodulator and the spectrum analysis moduleto operate simultaneously.
 2. The system of claim 1, wherein the AGCloop remains at a selected gain level for a predetermined hold timeafter a change in input signal power is detected by the AGC loop.
 3. Thesystem of claim 2, wherein the predetermined hold time is equivalent toa period of time sufficient for the spectrum analysis module to processa minimum number of fast Fourier transform (FFT) blocks at the selectedgain level.
 4. The system of claim 2, wherein the spectrum analysismodule designates an fast Fourier transform (FFT) block as suspect whenan AGC gain level change does not coincide in time with a boundary ofthe FFT block.
 5. The system of claim 4, wherein the spectrum analysismodule ignores FFT blocks that have been designated as suspect.
 6. Thesystem of claim 4, wherein the spectrum analysis module assigns lessweight to FFT blocks that have been designated as suspect compared toFFT blocks not so designated.
 7. The system of claim 4, wherein thespectrum analysis module relies on FFT blocks designated as suspect onlyfor detection but not for measurement.
 8. The system of claim 4, whereinan FFT valid signal indicates whether a given FFT block should bedesignated as suspect.
 9. The system of claim 2, wherein the gain levelchange is further delayed to align with a spectrum analysis event. 10.The system of claim 9, wherein the spectrum analysis event is a boundaryof a fast Fourier transform (FFT) block.
 11. The system of claim 1,further comprising a plots module and a classification module.
 12. Thesystem of claim 11, wherein different gain settling times are applied toat least two of the demodulator, the plots module and the classificationmodule.
 13. A system, comprising: a radio having a radio frequencyreceiver and a plurality of selectable automatic gain control (AGC)loops; a demodulator configured to demodulate wireless traffic receivedby the receiver; and a spectrum analysis module configured to performspectrum analysis of a frequency band over which the wireless trafficwas detected, wherein a given one of the selectable AGC loops isselected to favor operability of the demodulator or the spectrumanalysis module.
 14. The system of claim 13, wherein the demodulator andthe spectrum analysis module operate simultaneously.
 15. The system ofclaim 13, wherein one of the selectable AGC loops delays a change is AGCloop gain to accommodate fast Fourier transform (FFT) block processing.16. A method, comprising: receiving data at a wireless receiver;controlling an automatic gain control (AGC) loop associated with thereceiver such that the data is compatible with processing requirementsof both a demodulator and a spectrum analysis module; and passing thedata from the receiver to both the demodulator and the spectrum analysismodule.
 17. The method of claim 16, wherein the controlling comprisesmaintaining a given AGC gain level for a predetermined hold time after achange in input signal power is detected by the AGC loop.
 18. The methodof claim 17, wherein the predetermined hold time is equivalent to aperiod of time sufficient for the spectrum analysis module to process aminimum number of fast Fourier transform (FFT) blocks at a selected gainlevel.
 19. The method of claim 17, further comprising designating, assuspect, a fast Fourier transform (FFT) block when an AGC gain levelchange does not coincide in time with a boundary of the FFT block. 20.The method of claim 19, further comprising ignoring FFT blocks that havebeen designated as suspect.
 21. The method of claim 19, furthercomprising assigning less weight to FFT blocks that have been designatedas suspect compared to FFT blocks not so designated.
 22. The method ofclaim 19, further comprising: relying on FFT blocks designated assuspect only for detection but not for measurement.
 23. The method ofclaim 19, further comprising generating an FFT valid signal thatindicates whether a given FFT block should be designated as a suspectFFT block.
 24. The method of claim 17, further comprising extending thepredetermined hold time to coincide with a spectrum analysis event. 25.The method of claim 24, wherein the spectrum analysis event is aboundary of a fast Fourier transform (FFT) block.
 26. The method ofclaim 16, further comprising controlling a digital variable gainamplifier disposed between the receiver and the demodulator, but notbetween the receiver and the spectrum analysis module.
 27. The method ofclaim 16, further comprising controlling a digital variable gainamplifier disposed between the receiver and the spectrum analysismodule, but not between the receiver and the demodulator.
 28. Logicencoded in one or more tangible media for execution and when executedoperable to: simultaneously pass data from a receiver to both ademodulator and a spectrum analysis module; and control an automaticgain control (AGC) loop associated with the receiver such that the datais compatible with the processing requirements of both the demodulatorand the spectrum analysis module.
 29. The logic of claim 28 beingfurther operable to maintain a given AGC gain level for a predeterminedhold time after a change in input signal power at the receiver isdetected by the AGC loop.
 30. The logic of claim 29, wherein thepredetermined hold time is equivalent to a period of time sufficient forthe spectrum analysis module to process a minimum number of fast Fouriertransform (FFT) blocks at a selected gain level.